In a stapler incorporated in a copier or printer, on the one side of a feeding path along which the sheets after copied or printed are fed, a staple driving portion for driving a staple toward the sheets is arranged; and on the other side thereof, a clincher mechanism for bending legs of the staple penetrated the sheets and protruded on the lower side of the sheets along the rear surface of the sheets is arranged. In a clinching device of a general stapler conventionally known, a fixed clincher having a pair of guiding grooves formed on the upper end face for inwardly bending/guiding the staple legs is arranged on the rear side of the sheets, and the staple legs driven from the front surface of the sheets and protruded on the lower side of the sheets are engaged with these guiding grooves so that the staple legs are bent/guided inwardly.
In the clincher mechanism having the guiding grooves as described above, the staple is driven toward the sheets by a driver plate attached to the staple driving portion, and the staple legs penetrated the sheets and protruded on the rear side thereof are engaged with the above guiding grooves so that both legs are bent inwardly so as to form a curved loop shape at the base of the staple legs, thus stapling the sheets. In stapling by such a fixed clincher, the height of the loop shape formed at the base of both legs of the staple is much higher than the thickness of the sheets so that the thickness of the stapled portion becomes great. This led to a problem that when the stapled sheets are stacked, they will lean.
In order to avoid such an inconvenience, JP-A-10-128682 discloses a clincher mechanism equipped with a movable clincher which is engaged with the staple legs penetrated the sheets and protruded on the lower side of the sheets, thereby bending the staple legs along the rear surface of the sheets from the base side. In the clincher mechanism adopting such a movable clincher, the loop shape is not formed at the base of the staple legs so that the leaning of the sheets when they are stacked is avoided. However, a related driving mechanism for operating the movable clincher such as a cam or link is required so that the production cost of the stapler increases. Further, in an electric stapler in which the staple driving portion and the clincher mechanism are separately arranged so as put a sheet feeding path therebetween, a driving source such as another electric motor for driving the clincher must be provided. This leads to further cost increase.